Sirtuins are NAD+-dependent protein deacetylases that mediate adaptive responses to a variety of stresses, including calorie restriction and metabolic stress. Sirtuin 3 (SIRT3) is localized within the mitochondrial matrix, where it regulates acetylation levels of a diverse set of metabolic enzymes. Although well characterized in models of caloric restriction, relatively little is known about the role of Sirtuins and acetylaion under conditions of caloric excess. Our recent results show that when normal mice are fed a high fat diet they demonstrate reduced SIRT3 activity, impaired mitochondrial function, and hyperacetylation of a diverse set of proteins, including gluconeogenic enzymes, in their livers. Furthermore, SIRT3 knockout mice have signs of accelerated aging and cancer. Understanding SIRT3's biochemical function and regulation in the liver under conditions of caloric excess may potentially help explain the connection between reduced mitochondrial function and disorders of lipid and glucose metabolism, such as type 2 diabetes and nonalcoholic fatty liver disease (NAFLD). The immediate purpose of this proposal is two-fold: 1) determine if restoration of hepatic SIRT3 activity during high fat feeding can attenuate the progression of obesity- related steatosis or hepatic insulin resistance, and 2) Determine whether increasing hepatic NAD+, the major determinant of SIRT3 activity, will attenuate obesity-linked mitochondrial ROS and protein acetylation. The long-term goal of this project is to dissect the mechanisms surrounding how excess nutrients lead to hyperacetylation of key proteins and to identify a regulatory role for SIRT3 in NAFLD and susceptibility to type 2 diabetes. PUBLIC HEALTH RELEVANCE: Nonalcoholic fatty liver disease (NAFLD) is the most common nutritional disorder, currently affecting 50 percent of obese adults and 1/3 of obese children. Recent findings indicate that Sirtuin 3 (SIRT3) may play an important role linking hepatic fuel metabolism and mitochondrial health. The studies proposed here will investigate the role of SIRT3 as a promising target to protect against obesity-induced metabolic complications, including NAFLD. Findings from these studies will resolve whether altered SIRT3 activity contributes to the progression of obesity-induced liver steatosis, insulin resistance, and mitochondrial dysfunction, and determine if increasing SIRT3 activity can protect against (or at least minimize) these complications, providing valuable information for developing treatments for NAFLD.